Cell 1 Flashcards
What are the types of proteins in the plasma membrane?
Integral proteins- embedded in or pass through lipid bilayer
Peripheral proteins- associate with membrane lipids or integral membrane proteins
What are the 3 major classes of lipids? What percentage does each make up?
- Phospholipids (~75%)
- Cholesterol (~20%)
- Intercalates between phospholipids
- reduces membrane fluidity
- Glycolipids(~5%)
- Sugar-containing lipid molecules
- Found exclusively in outer monolayer
Describe plasma membrane lipids
~50% membrane mass
- Amphipathic
- Hydrophilic “water-loving” polar head
- Hydrophobic “water-fearing” nonpolar tail
Contrast integral and membrane proteins
- Integral membrane proteins
- transmembrane- single pass and multi pass
- Anchored
- alpha helix
- lipid chain
- oligosaccharide linker
- single pass and multi pass
- Peripheral membrane proteins
- Noncovalent association with integral membrane proteins
What are the general categories of integral membrane proteins?
- Pumps/carriers/transporters
- Channel
- Receptors
- Linkers
- Enzymes
- Structural proteins
Describe pumps/carriers/transporters as a category of integral membrane proteins
Transport specific ions across the membrane
- sodium
- Potassium
Transport metabolic precursors
- Amino acids
- Sugars
Describe channels as integral membrane proteins
Transport of ions, small molecules and water
-passive diffusion
Aqua porins
-water
Gap junctions
-passage of ions, small molecules between adjacent cells
What is the structure of the membrane ?
Fluid mosaic model
- fluid membrane
- lipids and proteins have ability to move within the plane of the membrane
What are the properties of the membrane?
Fluidity
- membrane lipids and proteins are mobile
- Cholesterol serves to stabilize the membrane
- Reduce membrane fluidity
Selective permeability
- Permeable
- Hydrophobic, non-polar, uncharged molecules
- oxygen, carbon dioxide
- Less permeable
- small, polar, uncharged molecules
- water
- highly permeable
- charged (ions), polar molecules
Transmembrane proteins
- channels and transporters
- increase the permeability of the membrane to molecules that cannot cross the lipid bilayer
What factors influenced diffusion?
- concentration gradient
- size or mass of the diffusing substance
- temperature
- surface area
- diffusion distance
Plasma membrane is a barrier to…
Diffusion
What is osmosis?
Diffusion of water across a semi-permeable membrane(doesn’t allow dissolved solutes to pass )
-movement from low solute concentration to high solute concentration
What is osmotic pressure?
- pressure that must be applied to prevent the flow of water across the semi-permeable membrane
- proportional to the concentration of the solute particles that cannot cross the membrane
What is osmoregulation?
Cellular mechanism to reach a balance in osmotic pressure/homeostasis
What is tonicity?
Measure of the osmotic pressure of 2 solutions separated by a semi-permeable membrane
What is an isotonic solution?
- equal concentration of solutes outside and inside of the cell
- homeostasis
What is an hypotonic solution?
- lower concentration of solutes outside than inside the cell
- Water enters the cell- cell swells and bursts (cytolysis)
What is a hypertonic solution?
- higher concentration of solutes outside the cell than the inside
- water exits the cell- cell shrinks(crenation)
What are the passive processes of membrane transport?
- simple diffusion
- diffusion through channel proteins
- facilitated diffusion
- carrier/pump/transporter
What are the active processes of me,Brahe transport?
- primary active
- secondary active
- vesicular
What are the types of membrane transport?
Passive and active processes
Describe diffusion through the lipid bilayer
- non-polar, hydrophobic molecules
- gases
- oxygen, carbon dioxide, nitrogen
Describe facilitated diffusion through channel protein
- polar, hydrophilic molecules
- inorganic ions
Give an example of facilitated diffusion via carrier protein
Glucose
What is primary active transport?
-energy requiring process that moves solutes against an electrochemical gradient
- sodium potassium pump
- important for regulating cell volume
Explain the functioning of the sodium-potassium pump
- 3 sodium ions from the cytosol bind to the inside surface of the sodium-potassium pump
- Na+ binding triggers ATP to bind to the pump and be split into ADP and P. The energy from ATP splitting causes the protein to change shape, which moves the sodium ions outside
- 2 potassium ions land to the outside surface of the pump and cause the P to be released
- The release of the P causes the pump to return to its original shape, which moves the K+ into the cell
What is secondary active transport?
- energy stored in one concentration gradient is used to drive other substances across the membrane against their own concentration gradient
- e.g. energy (ATP) used to build their Na+ or H+ gradient used to transport glucose or amino acids across
- use energy indirectly
- two types of transport: anti-porters and symporters
What are the types of vesicular transport?
Exocytosis and endocytosis
What is exocytosis
Substance exits the cell by the fusion of a vehicle with the plasma membrane
What is endocytosis?
Substance enters the cell by a vesicle formed from the plasma membrane
3 types:
- Receptor-mediated
- Pinocytosis
- Phagocytosis
What are the features of exocytosis?
- releases material from cells
- occurs in all cells
Especially important for:
-secretory cells
Ex. Enzymes, hormones, mucus
- nerve cells
- neurotransmitters
Explain the process of receptor-mediated endocytosis
- Binding
- ligand binds to specific receptor
- Clathrin recruitment - Vesicle formation
- clathrin dependent (makes a clathrin coated vesicle) - Uncoating (clathrin recycled)
- Fusion with endosome
- sorting of ligand and receptors - Degradation
- fusion with lysosome
What is pinocytosis ?
Pino= to drink
-bulk-phase endocytosis
- vesicle formation
- nonspecific
- invagination of membrane
- Clathrin dependent
- fusion with lysosome
- digestion
What is phagocytosis?
Phago= to eat
- large organic and inorganic particles
- bacteria, viruses, dead cells, debris
Explain the process of phagocytosis
- Binding
- ex. Antibody coated bacteria - Pseudopod formation
- actin dependent - Phagosome formation
- Fusion with lysosome
- Digestion
- lysosomal enzymes
What is cytosol?
- intracellular fluid: fluid portion that surrounds the organelles
- 55% of cell volume
What are the functions of cytosol?
Site of many chemical reactions
Mainly water with dissolved and suspended substances
-ions, glucose, fats, lipids, proteins, ATP and waste products
What are the microfilaments made of?
Made of the protein actin
G-actin
-free actin molecules in the cytoplasm
F-actin
- polymerized actin in a filament
- ATP dependent
Polarized structures
- fast growing (+) positive end
- slow growing (-) negative end
Microfilaments May exist as…
Single filaments, in bundles, or in networks
What are the cell functions of microfilaments?
- anchorage
- structural core of microvilli
- cell motility
- extension of cell processes
Describe the structure of intermediate filaments
Rope-like filaments
-structure= formed from non-polar and highly variable subunits
What are the functions of intermediate filaments?
Structural
- stabilize cell structure
- mechanical strength
- maintain the position
- Resist shearing forces
- extend across cytoplasm
- connecting with desmosomes and hemidesmosomes
Essential for integrity of cell-cell and cell-ECM junctions
Describe the structure of microtubules
Structure:
- Non-branching, rigid, hollow tubes
- a and B tubulin protein subunits - Polar
- Minus (-) end
- Plus(+) end
What are the functions of microtubules?
Intracellular transport
-movement of vesicles and organelles
Cell motility
- Movement of cilia and flagella
- Cell elongation and movement
Mitotic spindle
-Attachment of chromosomes & their movement during cell division
Rigid intracellular skeleton
-maintenance of cell shape and polarity
Assemble and disassemble as the needs of the cell change
Describe the structure of centrioles
- 9 triplets of microtubules arranged around a central axis
- Each triplet consists of 1 complete and 2 incomplete microtubules fused
What are the functions of centrioles?
-Organizes the Centrosome
- basal body formation
- provide basal bodies necessary for assembly of cilia and flagella
- Mitotic spindle formation
- formation of centrosome and alignment of the mitotic spindle during cell division
What is the structure of the centrosome ?
Contains a pair of centrioles
-arranged such that one is perpendicular to the other
Amorphous protein matrix
- >200 proteins
Gamma-tubulin ring complexes
-Nucleation sites for microtubules
What are the functions of centrosome?
Microtubules organizing center (MTOC)
Initiate microtubule formation
- microtubules are nucleated at the centrosome at their negative (-) ends
- Positive (+) ends point out and grow toward the cell periphery
What are the cilia and flagella?
These are microtubule structures
- motile
- beat in synchronous pattern
-9+2 microtubule arrangement
- pair of dynein arms
- motor protein
- binds adjacent microtubule
Anchored to cell via the basal body
-thin, dark-staining band at base of cilia
What is the function of cilia and flagella?
Move fluid and particles along epithelial surfaces
What is the rER?
Membrane bound ribosomes attached to cytoplasmic surface of the ER
- Abundant in cells specialized in protein synthesis
- Ex. Secretory cells producing proteins for extracellular export
What is the sER?
-region of the ER that lacks bound ribosomes
- abundant in cells specialized in lipid metabolism
- well developed in cells that synthesize and secrete steroids
What are the functions of sER?
Plays a major role in detoxification
-ex. Heoatocytes
Also functions to sequester calcium
-ex. Muscle cells and sarcoplasmic reticulum
What is the Golgi apparatus?
- complex of flattened, membrane-enclosed cisternae
- usually located next to the nucleus and centrosome
- each Golgi stack had 2 faces
Cis face= entry
-receives vesicles from rER
Trans face= exit
What are the functions of the Golgi apparatus?
- post transnational modifications
- glycisylation
- phosphorylation
- sulfation
Sorting
Packaging
What are the 3 destinations of the Golgi apparatus?
Lysosomal vesicles
Secretory vesicles
Membrane vesicles
What are lysosomes
Digestive organelles
Membrane-enclosed compartments filled with ~40 types of hydrolytic enzymes
Whaat is the function of lysosomes?
Controlled Intracellular digestion of macromolecules
Describe the structure of the mitochondria
2 membranes- outer and inner membrane
2 compartments - inter membrane space and matrix
What are the functions of the mitochondria?
Generate ATP
-citric acid cycle
-oxidative phosphorylation
— B-oxidation of fatty acids
Abundant in cells that generate and expend large amounts of energy
-ex. Striated muscle cells
Evolved from aerobic bacteria that were engulfed by primitive eukaryotic cells
- Have own DNA
What are peroxisomes?
Microbodies
-small organelles (0.5 um diameter)
What are the functions of peroxisomes ?
Specialized to compartmentalize and degrade toxic reactive oxygen molecules
- contain catalase and other peroxidases
- converts hydrogen peroxide to oxygen and water
- particularly important in hepatocytes
- detoxification of ingested alcohol
